The human heart is a concave muscular organ, consisted of two atria and two ventricles, right and left. The atria communicate with the ventricles with the atrioventricular valves. The left atrium communicates with the left ventricle through the mitral valve and the right atrium communicates with the right ventricle through the tricuspid valve. At the output of the left ventricle, there is the aortic valve and at the output of the right ventricle there is the pulmonary valve. The function of the valve is to allow the one way flow through them. The valves consist of leaflets, three in number, apart the mitral valve where consists of two leaflets. The leaflets open to allow the blood to pass through them and close to prevent the regurgitation.
There are conditions that this mechanism fails with the result of non-physiological flow through them. In some congenital or acquired diseases, there is a hardening of the leaflets, more commonly due either to calcification or to rheumatic fever, which results to difficulty of fully opening of the leaflets and passing the blood through them. In these circumstances, the patient presents with the symptoms of valve stenosis.
In some circumstances, the leaflets do not come in conduct when they close, which results to blood leakage and the patient presents with the symptoms of valve regurgitation. In severe circumstances of stenosis or regurgitation, the diseased valve has to be replaced with a new prosthetic valve.
There are mainly two types of prosthetic valves for replacement: the mechanical and the biological. The mechanical valves has movable parts, mainly from graphite, while the biological valves are derived either from porcine aortic valve, or bovine pericardium (E. Andreas Agathos, Albert Starr: “Aortic Valve Replacement”, Curr Prob Surg, July 1993: Vol XXX, No 357, pp 610-637), or from the aortic, pulmonary and the pericardium derived from seals (E. Andreas Agathos, “Human Cardiac Valve Placement with Marine Mammal Ventricular Outflow (Aortic or Pulmonary) Valves, U.S. Pat. No. 6,165,216, issued Dec. 26, 2000, and E. Andreas Agathos, “Human Cardiac Valve Replacement with Seal's Cardiac Valve (Aortic or Pulmonary), Greek patent No 1005718, issued on Jul. 11, 2007.
The bioprosthetic valves show an advantage over the mechanical valves, as they do not need the daily intake of anticoagulants, thus producing less incidence of thromboembolic episodes, hemorrhage and infectious endocarditis. The main disadvantage though is that they do not last as long as the mechanical valves do.
The bioprosthetic valves need a support system (stent) made of biomaterial, onto with the animal tissue is placed. There are many methods of placing animal tissue on a support system such as “Method of Leaflet Attachment for Prosthetic Heart Valves”, U.S. Pat. No. 4,501,030, issued Feb. 26, 1985, “Tissue Heart Valves and Stent”, U.S. Pat. Nos. 5,163,955, 5,423,887 and 5,489,298 to Love et al and “Prosthetic Heart Valve with Slit Stent”, U.S. Pat. No. 6,936,067, issued on Aug. 30, 2005 to Buchanan; Eric S.